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Fluorescence Quenching and Copper Complexation by a Chestnut Leaf Litter Extract: Spectroscopic Evidence
Author(s) -
Sposito Garrison,
Holtzclaw Kenneth M.,
Senesi Nicola
Publication year - 1988
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1988.03615995005200030006x
Subject(s) - chemistry , carboxylate , copper , quenching (fluorescence) , electron paramagnetic resonance , fluorescence , fluorescence spectroscopy , infrared spectroscopy , molecule , inorganic chemistry , aqueous solution , nuclear chemistry , stereochemistry , organic chemistry , nuclear magnetic resonance , physics , quantum mechanics
Fluorescence quenching on addition of Cu(II) to aqueous solutions of chestnut ( Castanea sativa L.) leaf litter extract (LLE) has been interpreted previously in terms of Cu complexation by LLE organic ligands. In order to provide direct evidence for the existence of these complexes, as well as information about their coordination structures, infrared (IR) and electron spin resonance (ESR) spectroscopy were applied to investigate Cu/LLE mixtures that showed increasing fluorescence quenching with increasing pH. The Cu/LLE mixtures were prepared with approximately equimolar concentrations of Cu and LLE binding sites (200 mmol m −3 ) at pH values in the range 4 to 7. The IR spectra indicated the existence of Cu complexes involving carboxylate groups, even at pH 4. The more sensitive ESR spectra showed that Cu(II) could displace Fe(III) and Mn(II) from LLE binding sites, and that inner‐sphere complexes between Cu and LLE ligands were formed. These complexes involved carboxylate ions and H 2 O molecules at pH < 6, and both O‐ and N‐containing ligands at pH 6 and 7. These results confirmed the hypothesis that fluorescence quenching is associated with strong Cu complexation by organic ligands in the LLE.